Need to get repository [repomd.xml] to work

I have a machine I just loaded Centos 5.5 on and being a newbie on Lilnux the program manager was working and now it isn't working. Also have updates that are waiting but can not get them. How do I get repomd.xml to work. The message says this: Cannot retrieve repository metadata (repomd.xml) for repository c5.media. Please verify its path and try again.

Please advise what to do about this. Is there a command line that I need to enter into the terminal command to get it to work again and what is it. Thanks guys for the answer.